Browsing by Author "Lin, C. -P."

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Apparent Dielectric Constant and Effective Frequency of TDR Measurements: Influencing Factors and Comparison
(2009-08-01)
Chung, C. -C.
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Lin, C. -P.
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土木工程學系
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Department of Civil Engineering
When measuring soil water content by time domain reflectometry (TDR), several methods are available for determining the related apparent dielectric constant (K(a)) from the TDR waveform. Their influencing factors and effective frequencies have not been extensively investigated and results obtained from different methods have not been critically compared. The purpose of this study was to use numerical simulations to systematically investigate the effects of electrical conductivity, cable length, and dielectric dispersion on K(a) and the associated effective frequency. Not only does the dielectric dispersion significantly affect the measured K(a), it also plays an important role in how K(a) is affected by the electrical conductivity and cable length. Three methods for determining K(a) were compared, including the dual tangent, single tangent, and derivative methods. Their effective frequencies were carefully examined with emphasis on whether the effects of electrical conductivity, cable length, and dielectric dispersion can be accounted for by the estimated effective frequency. The results show that there is no consistent trend between the change in K(a) and the change in effective frequency as the influencing factors vary. Compensating the effects of electrical conductivity, cable length, and dielectric dispersion by the effective frequency seems theoretically infeasible. To improve the accuracy of TDR soil water content measurements in the face of these influencing factors, future studies are recommended toward TDR dielectric spectroscopy or developing signal processing techniques for determining the dielectric permitivity near the optimal frequency range.
Clarification and calibration of reflection coefficient for electrical conductivity measurement by time domain reflectometry
(2008-07-01)
Lin, C. -P.
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Chung, C. -C.
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Huisman, J. A.
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Tang, S. -H.
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土木工程學系
Measurement of electrical conductivity by time domain reflectometry (TDR) requires knowledge of the source step voltage, which is often implicitly accounted for in the measured reflection coefficient. Errors may arise, however, from imperfect amplitude calibration when transforming the voltage signal into the reflection coefficient signal. This instrument error was identified as a considerable source of error in addition to cable resistance for TDR electrical conductivity measurements. The effect of the instrument error due to imperfect amplitude calibration was theoretically examined by the direct current circuit model and experimentally verified. The instrument error resulted in an overestimation of electrical conductivity while the cable resistance led to an underestimation. We clarified that the series resistors model for correction of cable resistance is accurate if the measured reflection coefficient is corrected for the instrument error. A calibration (correction) method for the measured reflection coefficient was proposed to account for both the instrument error and the effect of cable resistance, leading to a simple, accurate, and theoretically sound procedure for TDR electrical conductivity measurements.
Performance enhancement of the nMOSFET low-noise amplifier by package strain
(2007-01-01)
Hua, W. -C.
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Chang, H. -L.
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Wang, T.
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Lin, C. -Y
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Lin, C. -P.
The package strain improves the noise figure (NF) of the low-noise amplifier (LNA). The maximum noise reduction is similar to 0.53 dB (13%) at the operating frequency of 2.4 GHz under the biaxial tensile strain of 0.037%. The NIT reduction of the strained LNA is mainly due to the enhanced transconductance and cutoff frequency of the individual nMOSFET device under the same strain and bias conditions.